Impact universal joints are used for installing and removing fasteners or other driven workpieces. This is necessary where straight (0.degree. offset) access is difficult or impossible. There are numerous industrial applications. The average citizen most commonly encounters impact universal joints in the automobile garage where the mechanic uses the socket with a power driver to remove and install lug nuts on the wheels of the automobile. The power driver with the impact universal joint provides a means to apply torque to the workpiece and to periodically add an impact to further rotate the workpiece.
Impact universal joints have been known for many years with only a single design dominating the market. This is the "pin and ball" design. In these devices, a ball is received in a torque and impact socket and a pin is disposed in the wall of a socket and through a slot in the ball. The assembly is spring loaded between the ball and the socket interior bottom. The forces on the device are carried, in shear, by the cross-sectional area of the pin. Under the impact and torsinal forces applied, the pin is the most likely member to fail. Increasing the diameter of the pin reduces failure of the pin but causes the slot in the ball to be widened, which decreases the cross-sectional area of the ball which then weakens the ball and becomes a failure point (U.S. Pat. No. 2,441,347 to Dodge).
In U.S. Pat. No. 4,188,801, Hugh et al use a quadrified ball in a square socket. However, in this universal joint, all of the load is carried by the quadrified ball. A force vector analysis shows that the forces are directed to the socket in a manner which applies a significant portion of the forces in a radial direction as opposed to a tangential direction necessary to turn the socket. This applies unwanted radial expansion loads to the sides of the socket and reduces the amount of torque and impact transmitted.
The applicant is also aware of other tools which utilize spherical coaxial members such as U.S. Pat. No. 3,775,997 to Carman, U.S. Pat. No. 5,503,236 to Tibbitts and U.S. Pat. No. 5,573,463 to Arlt. Carman and Tibbitts disclose teeth or lands which are formed on the sphere but are too costly for the consumer tool market.
U.S. Pat. No. 919,651 to Spicer discloses a universal joint which is calculated to withstand heavy pressure due to the transmission of heavy loads with joint members at a considerable angle. The head has spherical curvature. Bearing boxes are arranged to slide in portions of the transverse slot, the sides of said portions serving as guides for the boxes. The bearing boxes are shoes for pivot pin, and, where very light loads are to be transmitted, may not be required with pin sliding and pivoting on guides of a member.